The current WC (water closet) is an irresponsible lots of water swallowing sanitary furniture for rinsing manure through our mileage sewage to giant treatment plants. Per day a man here uses 35 liters of clean drinking water or rainwater to flush. In a year so that makes 12,275 liters of drinking water.
Put a brick in your toilet sink. Or a bottle with water. This saves each time the same volume of water. With every puddle flushing is certainly not necessary.

A septic tank
This is an underground reception pit with a septum and a landing. In this system, sink or float the solids (sludge) in the tank, while the liquids pass through a filter with overflow into the drains or drainage system.
The sludge is completely degraded by bacteria. If too much water enters (by connecting also bathroom, kitchen, downspouts) the bacteria haven’t enough time to do their destructive work, and you get a tank full of stinking mud that needs to be emptied.
Soap, medications, antibiotics, solvents etc. can inhibit bacterial life, distort and even completely destroy it.

A toilet was until a few decades ago a cottage above the cesspool, a ditch or a hole in the ground.
Stools were also done in a pot or bucket and ended up using cesspool or manure pile in the fields. As still are being used in most of the world. Also with animal urine and dung. Finally, the human being is a mammal, but just as any other.

A comfortable wooden toilet seat from around the year 0 was discovered in the deep pre-hadrianic canals on Vindolanda.